A wafer prober is a device for connecting a plurality of chips on a wafer to a tester. Such a tester is connected to the chips on the wafer through the wafer prober and is configured to provide electrical signals to the chips and inspect the results of provision, thus examining whether abnormalities or defects are present in each of the chips. The construction and operation of the wafer prober are described in brief with reference to FIG. 1. When a wafer 209 on which a plurality of chips is formed is loaded into a chuck plate 208 through a wafer transferring device 204, the chuck plate 208 is transferred in X, Y and Z directions so that a plurality of probes provided in a probe card 210 is aligned and put into contact with pads on the plurality of chips provided on the wafer through a chuck transferring device 206. Here, the X and Y directions denote a direction horizontal to the surface of the chuck plate, and the Z direction denotes a direction perpendicular to the surface of the chuck plate. When the plurality of probes comes into contact with the plurality of pads, respectively, a tester 100 provides test signals corresponding to a predetermined program to the chips through tester connection terminals and the probes, and the chips provide output signals corresponding to the test signals to the tester 100, thus testing each chip for electrical characteristics.
Hereinafter, with reference to FIG. 2, an embodiment of a mechanical component for vertically transferring the chuck plate 208 will be described below.
A wedge-shaped support 212, one surface of which is cut in an inclined shape, is installed on the bottom surface of the chuck plate 208, and a wedge-shaped Z axis transferring unit 216, one surface of which is cut in an inclined shape, is arranged at the location opposite the inclined surface of the support. A rolling bearing 214 is interposed between the support 212 and the Z axis transferring unit 216 to reduce friction therebetween. Here, the inclined surface of the Z axis transferring unit 216 is formed to have a shape corresponding to the inclined surface of the support 212. The inclined surface of the Z axis transferring unit and the inclined surface of the support are arranged opposite each other. A ball screw 218 is installed below the Z axis transferring unit 216, and is configured to move the Z axis transferring unit 216 in a laterally direction while rotating in association with a Z axis motor 220. As the Z axis transferring unit 216 is moved in the lateral direction, the height of the inclined surface of the support 212 facing the Z axis transferring unit 216 is changed. In this way, with the lateral movement of the Z axis transferring unit 216, the chuck plate 208 is vertically transferred. Further, a Z axis base 222 is installed below the Z axis transferring unit to support the bottom of the wafer prober. The Z axis transferring unit 216, the ball screw 218 and the Z axis motor 220 are arranged on the Z axis base 222. The motor 220 produces a predetermined torque used to transfer the Z axis transferring unit 216.
However, the motor may produce an excessive torque due to an unexpected disturbance. In this case, the chuck transferring device excessively transfers the chuck plate in a vertical direction, so that the wafer put on the chuck plate 208 may come into excessively close contact with the probe card, thus causing damage to the wafer and the probes of the probe card. Therefore, in the prior art, the development of technology for determining whether excessive pressure is being applied to the Z axis transferring unit 216 or the chuck plate, and discontinuing transferring the chuck plate in a vertical direction if it is determined that excessive pressure is being applied, is required.
Further, in order to bring the fine pads formed on the wafer into precise contact with the probes of the probe card 210, the control of the position of the chuck plate 208 is very precisely performed, and thus the chuck plate is precisely installed in consideration of a horizontal state. However, there is a problem in that the Z axis base 22 for supporting the Z axis transferring unit 216 may be tilted due to an unexpected disturbance during the use of the wafer prober, thus making it difficult to maintain the chuck plate in a horizontal state. As a result, the development of technology for detecting the tilting of the Z axis transferring unit 216 and correcting the tilting of the chuck plate is required in the prior art.